There is known an engine of a vehicle provided with a throttle control apparatus having an electrically operated throttle valve. For example, a throttle control apparatus 202 is shown in FIG. 7 wherein an electrically operated throttle valve 204 is installed in an intake path 206 and the throttle valve 204 is operated by a motor 208 for throttle movement. The throttle driving motor 208 communicates with a throttle control unit 210-1 of a control means 210.
To carry out a failsafe operation, a sensor system with a twofold or redundant detecting structure is provided. The throttle control apparatus 202 includes first and second throttle position sensors 212-1 and 212-2, and first and second accelerator position sensors 216-1 and 216-2 communicating with an accelerator pedal 214. The motor 208 for throttle movement includes first and second motor drive coils 218-1 and 218-2.
The first throttle position sensor 212-1 communicates with the throttle control unit 210-1 through a power source supply line 220-1, a ground line 222-1 and an electrical signal output line 224-1. The second throttle position sensor 212-2 communicates with the throttle control unit 210-1 by an electrical signal output line 224-2.
The first accelerator position sensor 216-1 communicates with an engine control unit 210-2 by a power source supply line 226-1, a ground line 228-1 and an electrical signal output line 230-1. The second accelerator position sensor 216-2 communicates with the engine control unit 210-2 by a power source supply line 226-2, a ground line 228-2 and an electrical signal output line 230-2.
The first motor drive coil 218-1 communicates with the throttle control unit 210-1 by a power source supply line 232-1 and a ground line 234-1. The second motor drive coil 218-2 communicates with the throttle control unit 210-1 by a power source supply line 232-2 and a ground line 234-2.
Thereby, when a sensor communication route of any one of the first and second throttle position sensors 212-1 and 212-2, the first and second accelerator position sensors 216-1 and 216-2 or the drive coils 218-1 and 218-2 fails, the driver is informed of the failure by lighting a failure display lamp 236. There is also installed a throttle wire 238 for escape vehicle running during a failure by which the throttle valve 204 is operated such that the vehicle can be driven to a service station. In this case, when one sensor communication route fails, then, for example, there are cases in which supply of power source to the motor 208 for throttle driving is stopped and the vehicle is run at a default opening degree mechanically provided to the throttle valve 204. That is, the throttle is fixed with a throttle opening degree .theta.=15.degree., or the throttle valve 204 is mechanically operated via the throttle wire 238 for escape running.
Further, such a failsafe sensor structure is disclosed in, for example, Japanese Patent Laid-Open No. 99058/1993 or Japanese Patent Laid-Open No. 209809/1997. According to the structure described in Japanese Patent Laid-Open No. 99058/1993, there are provided two detecting means for detecting the operating state of a vehicle and operating control of the vehicle is carried out in accordance with an output state of the detecting means. When both of the detecting means are determined to be normal, an object of the control is further safely controlled. According to the structure described in Japanese Patent Laid-Open No. 209809/1997, there are installed multifold detecting means, and in determining detection signals, a determination is carried out in accordance with whether the changing speed of respective detection values fall in reference ranges to thereby promote certainty and conformity of failsafe.
In the throttle control apparatus having two control circuit routes, when one of the control circuits fails, throttle control is carried out by using the other control circuit. However, when one of the two control circuit routes fails (or may be described otherwise as "determined to fail"), there is a high possibility of its being accompanied with other failure in respect to an engine controller or a throttle controller of the control means and when normal throttle opening degree control is carried out, this a concern of causing unnecessary throttle operation in running the vehicle and an improvement has been desired.
However, according to a conventional throttle control apparatus, in the case of a failure of a onefold (i.e., non-redundant) sensor, the throttle control apparatus carries out a corresponding failsafe control when the sensor system fails. Main functions of the failsafe control are notifying an abnormality to the driver by turning on a malfunction indicating lamp (MIL) when the sensor system fails and carrying out a simplified control for escape running such that a vehicle can be driven to a service station which can repair the vehicle.
The function of carrying out the simplified control for escape running can be explained as a function that places a power source of the throttle driving motor in an OFF state when the sensor system fails and allows the vehicle to run with the throttle valve being at a default opening degree mechanically provided to it (for example, opening degree is fixed to 15 degree). Thus, it is intended to run the vehicle by setting the throttle valve to the default opening degree, the vehicle is run regardless of the intention of the driver and, accordingly, there is an inconvenience in which needed depression force exerted on a brake pedal is increased, and a strange feeling is caused in running the vehicle.
Further, in an apparatus which does not carry out the simplified control for escape running, there is an apparatus provided with an auxiliary wire for escape running. According to this construction, the throttle opening degree of the throttle valve is mechanically opened and closed by the wire to thereby enable running when the sensor system is failed. Moreover, when the vehicle is run by mechanically operating the throttle valve with the throttle wire for escape running, there are inconveniences in that the throttle wire and peripheral parts are needed, the number of parts is increased, the construction is complicated and the apparatus becomes increasingly expensive.